1. Field of the Invention
The present invention relates to an image pickup apparatus having a multi-stage retractable lens barrel.
2. Description of the Related Art
An image pickup apparatus, such as a digital still camera and a video camera, needs a high magnification of an image pickup lens and a miniaturization of a lens barrel configured to house the image pickup lens is required.
Japanese Patent Laid-Open No. (“JP”) 2004-198499 discloses a lens barrel having a so-called two-stage retractable structure. In this lens barrel, a straightforward movement cylinder moves in an optical axis direction which includes three cam followers engaged with three cam grooves in a surrounding wall of a rotational cam ring (fixation/movement cylinder) as a rotation of the motor is transmitted to the rotational cam ring via a cylindrical gear and the rotational cam ring rotates. Since the three cam followers of the rotational cam ring are engaged with three cam grooves in the surrounding wall of the rotational cam ring, the rotational cam ring moves in the optical axis direction while the rotational cam ring rotates. Thereby, a two-stage retractable lens barrel can be realized in which the straightforward movement cylinder and the rotational cam ring can project from and retract into the fixation cam ring (or the image pickup apparatus body).
The lens barrel disclosed in JP 2004-198499 has a perforation groove used to arrange the cylindrical gear on the surrounding wall of the fixation cam ring. In addition, the cam ring in the optical axis direction is long in order to form three cam grooves of the above fixation cam ring in the surrounding wall of the fixation cam ring outside the perforation groove at regular intervals in the circumferential direction.
In order to shorten the length of the fixation cam ring in the optical axis direction, one of the three cam grooves, for example, may be formed so that its partial area can be eliminated by the perforation groove. However, when the cam follower is slipped off from the cam groove in the imperfect area (non-engagement area), the rotational cam ring is likely to incline or decenter relative to the optical axis even when the other cam followers are engaged with the other two cam grooves.